1. Field of the Invention
The invention relates to a method for microwave measurement of an object to be measured, at least the surface of which is made of an electrically conductive material. The invention also relates to a measuring device and an oscillator.
2. Description of the Related Art
In an electrically conductive, usually flat piece the thickness of the piece and/or also some other dimension parallel with its thickness may be measured using microwave measurement in which the resonance frequency of the measurement resonator depends on a thickness dimension of the piece to be measured. For example, a cylindrical resonator or a Fabry-Perot resonator may be used for this purpose. The resonator frequency can be found by scanning the frequency of an oscillator producing microwave radiation over a measurement band. The thickness dimension of the piece to be measured can then be determined as a function of the found resonator frequency.
However, frequency scanning involves a number of problems. A measuring device based on frequency scanning is complicated and expensive, because it requires scanning electronics that change the oscillator frequency. In addition, frequency scanning is time-consuming, because the measurement must be carried out at all measurement band frequencies and thus it takes time before the measurement results are obtained. Measuring the thickness of a moving and shaking plate by means of a frequency scanning application is problematic, because it is not possible to carry out a rapid, synchronic and perfectly simultaneous measurement of distance on both sides of the plate.